Ethanol is a ubiquitous polar protic solvent in biochemistry and molecular biology. It plays a central role in nucleic acid precipitation, sample sterilization, and extraction of polar metabolites due to its complete miscibility with water and its ability to modulate solvent polarity. Its physicochemical properties make it indispensable in both routine laboratory workflows and advanced molecular applications.

Chemical Properties

Ethanol (C₂H₅OH) contains a primary alcohol functional group attached to a two-carbon chain. The molecule exhibits sp³ hybridization with a tetrahedral geometry and a C–O–H bond angle of approximately 109°. It has a boiling point of 78.4°C and a density of 0.789 g/mL at 20°C. Fully miscible with water (dielectric constant 24.5), ethanol forms hydrogen bonds and azeotropic mixtures, enabling efficient disruption of biomolecular hydration shells. Molecular biology grade ethanol (>99.5%, nuclease-free) ensures minimal DNase and RNase contamination, which is critical for nucleic acid applications.

Biochemical Applications

In molecular biology workflows, 70–100% ice-cold ethanol is widely used to precipitate DNA and RNA from aqueous solutions. The addition of salts such as 0.1–2.5 M ammonium acetate enhances selectivity and recovery efficiency, often exceeding 80%, by reducing nucleic acid solubility through dielectric constant lowering. This step is fundamental for downstream applications including PCR, cloning, and NGS library preparation.

In lipid biochemistry, ethanol is incorporated into extraction protocols such as modified Bligh-Dyer methods to solubilize phospholipids prior to chloroform phase separation. It is also used to wash Folch phases for ganglioside recovery. In protein analysis, ethanol serves as a fixing agent for gels prior to staining and as a dehydrating agent in histological preparations, while preserving antigenic epitopes for immunofluorescence assays.